Conventional medical therapies for CNS disorders, both surgical and pharmacological, often have widespread unwanted effects on brain areas not involved in the disorder being treated. In response to this we are developing what we have termed "molecular neurosurgery". Molecular neurosurgery is a novel approach to nervous system disorders that uses genetically modified viruses to modulate cells in the nervous system. Stereotactic local delivery permits modulation of a geographically defined cell population whereas the viral design can allow for cell specificity and expression of large molecules. The long term goal of this project is to deliver an engineered transcription unit (transgene) encoding glutamic acid decarboxylase (GAD) to primary neural cells in culture and to discrete locations in the brain, via defective herpes simplex virus (HSV) vectors. It is proposed that this will increase the biosynthesis of gamma-aminobutyric acid (GABA) and/or increase glutamate degradation. A novel set of GAD transgene vectors will be constructed that will permit detection and characterization of the transgene product in vivo. The in vitro experiments will allow us to characterize the extent of GAD transgene expression and its influence on the metabolism of GABA and glutamate in various cell-types including glia and glutaminergic and GABAergic neurons. We will test our ability to modulate GABA synthesis in vivo using a rat model of complex partial seizures, the "area tempestas". In vivo delivery of the GAD transgene into a crucial seizure-triggering locus in the deep prepiriform cortex (area tempestas) or into a key site of GABA-mediated anticonvulsant action in the midbrain (substantia nigra) will allow us to evaluate the functional impact of this site-directed gene therapy. These techniques will be useful for basic neurobiological studies of epilepsy and GABA/glutamate metabolism. Eventually, they will form the basis for a new form of epilepsy treatment and as a model for molecular neurosurgery of other disorders. Over 2 million Americans suffer from epilepsy of which approximately 25% are refractory to drug treatment and are candidates for surgical therapy. Other nervous system disorders also amenable to molecular neurosurgery include neurodegenerative disorders, genetic disorders such as Huntington's chorea, pain modulation and biochemically- based psychiatriC disorders. This proposal combines the skills of neurosurgery for highly localized application, molecular biology for the creation of defective herpes vectors, and pharmacology for the modeling of epileptic seizures and studies of combined local and systemic modulation.